Dietary arachidonic acid supplementation improves the growth performance and alleviates plant protein‐based diet‐induced inflammation in juvenile turbot ( Scophthalmus maximus L.)

A 56-day feeding trial was conducted to investigate the effects of arachidonic acid (ARA) supplementation on growth and immunity of plant protein-fed turbot (Scophthalmus maximus L.). Five isonitrogenous and isoenergetic diets were formulated, including fishmeal group (0.6 g/kg ARA), plant protein group (0.2 g/kg ARA) and plant protein groups supplemented with ARA (2.6, 7.4 and 11.8 g/kg ARA). Results showed that replacement of dietary fishmeal by plant protein blend significantly inhibited weight gain rate (WGR) from 511.53 ± 2.92% to 399.32 ± 5.40%. The specific growth rate (SGR) and final body weight (FBW) were also reduced. However, supplying ARA up to 11.8 g/kg could restore the WGR, SGR and FBW to the similar levels with FM group (p > .05). In addition to decreasing nutrient digestibility and distal intestinal morphology, the plant protein-based diet also attenuated innate immune enzyme activity and triggered intestinal inflammation, which were significantly improved by ARA supplementation. Dietary ARA restored the expression of the anti-inflammatory cytokine (transforming growth factor-β) and reduced pro-inflammatory cytokine (tumour necrosis factor-α, interleukin-1β and interleukin-8) mRNA levels. Taken together, ARA supplementation in the plant protein-based diet could improve growth performance and alleviate intestinal inflammation caused by dietary plant protein in juvenile turbot.